Relay-transistor flasher



1, 1965 H. KRATOCHVIL RELAY-TRANSISTOR FLASHER Filed Dec. 10, 1962 INVENTOR A44R2v/(Aw-mc/W/4 BY Q 111M (names ATTORNEYS United States Patent Ofiice 3,204,146 Patented Aug. 31, 1965 3,204,146 RELAY-TRANSISTOR FLASHER Harry Kratochvil, Fords, NIL, assignor to Tung-Sol Electric Inc., a corporation of Delaware Filed Dec. 10, 1962, Ser. No. 243,497 3 Claims. (Cl. 315-209) The present invention relates to heavy duty flashers of the type used on cabs of trailer trucks and the like and comprises a simple sturdy flasher that is not sensitive to variation in load, is insensitive to temperature fluctuation and has a long useful life.

Hot wire flashers of the type disclosed and claimed in Schmidinger Re-issue Patent No. 24,023, now abandoned, are in general use in the industry for flashing directional signals in passenger cars. Such series type flashers are well suited for use where the load is constant. However, in the case of trucks where the number of lights to be flashed may vary widely the series type hot wire flashers are not suitable The flasher of the present invention comprises a relay and a transistor coupled together for control of the energization of the relay in response to conductivity of the transistor. A capacitor, connected across the collector-base diode of the transistor is alternately charged and discharged by a circuit dependent upon position of the relay contacts to control the transistor and cause intermittent conduction through the tran sistor with corresponding intermittent energization of the relay. The contacts of the relay, when energized, close the circuit for the load and thus flash lamps in the load. A thermistor in the charging circuit of the capacitor makes the flashing rate insensitive to ambient temperature.

For a better understanding of the invention and of a specific embodiment thereof, reference may be had to the single figure of the drawing in which the preferred embodiment of the flasher of the invention is shown connected in a circuit for control of a lamp load.

Referring to the figure, the flasher is shown in a circuitwhich includes a car battery 12, a turn indication selector switch 14, and two sets of lamps 16 and 18 which may be, respectively, the right and left turn signal lamps.

The flasher 10 is mounted in a metal case diagrammatically represented by the dashed enclosure 20. Two terminals 22 and 24 of the flasher are isolatedly mounted in the case 20. The input terminal 22 is connected to the positive terminal of the battery 12 and the output terminal 24, is connected to the movable arm of switch 14.

The arm of switch 14 can be electrically connected to any of three contacts by positioning lever 26. One of these contacts is open, the other two contacts are wired to the turn indication lamps 16 and 18. The negative terminal of the battery 12, the flasher case 20, and the other terminals of the lamps 16 and 18 are connected to the car chassis 28 which serves as ground for the system.

In the flasher 10 there is a relay 30 with a single set of contacts. The armature 32 of this relay is connected to the input terminal 22 and the normally open contact 34 of the relay is connected to the output terminal 24 so that when the relay is energized the armature and the normally open contact complete a circuit between the battery and the movable arm of the switch 14.

In addition to the relay 30, the flasher 10 inclues a circuit, incorporating the coil 36 of the relay, for controlling the energization and de-energization of the relay. In this circuit, one end of the coil 36 is connected through the input terminal 22 to the battery 10 and the other end of the coil 36 is connected to the emitter of a p-n-p transistor 38. The collector of this transistor is attached to the grounded metal case 20 to complete a series circuit including the battery 12, the coil 36 and the transistor 38.

With this series circuit the relay 30 is energized when the transistor is conducting and de-energized when the transistor is rendered non-conducting. For control of the conduction of the transistor, a capacitor 40 is connected across the base-collector diode of the transistor 38 and a number of resistors are provided for charging and discharging the capacitor 40. These resistors include a first resistor 42 connected between the base of the transistor and the normally open contact 34 of the relay, a second resistor 44 and a thermistor 46 in parallel with the first resistor 42, and a third resistor 48 connected between the armature 32 and the normally open contact 34 of the relay. A fourth resistor 50 is connected between the emitter and the grounding casing 20 for a purpose which will be discussed hereinafter.

In operation, when the relay 30 is de-energized and the arm of switch 14 is at the open contact, the capacitor 40 is charged by the battery 10 through the thermistor 46,

and the first, second, and third resistors 42, 44 and 48.

When the capacitor 40, charges sufliciently, the voltage level at the base of the transistor back biases the baseemitter junction of the transistor rendering the transistor non-conductive. With the transistor 38 non-conductive, the current flowing through the coil 36 is insufficient to keep the relay energized. As long as the arm of the switch is at the normally open contact, there is no path through which the capacitor may be discharged so that the capacitor remains charged preventing energization of the relay.

Now if the arm of the switch 14 is positioned for a right turn indication, the lamps 16 are connected through the switch 14 to the normally open contact 34 of the relay. As the resistance of unlighted lamps is very low the potential at contact 34 will drop almost to ground potential. Capacitor 40 will thus discharge through resistors 42 and 44, thermistor 46 and lamps 16. When the charge on the capacitor is reduced sufliciently to forward bias the base-emitter junction of transistor 38 the transistor will conduct and increase the current flow through the coil 36 to energize the relay 30.

Energization of the relay moves the armature 32 against the normally open contact 34 to bypass resistor 48 and apply the full potential of the battery 12 across the lamps 16. This lights the lamps 16 and in addition starts capacitor 40 charging through resistors 42, 44 and thermistor 46. The capacitor continues to charge until the voltage at the base again increases sufliciently to reduce the bias of the base-emitter junction of the transistor and decreases the flow of current through the transistor. With this the relay is de-energized and therefore breaks the contact between its armature 32 and normally open contact 34 to reinsert resistor 48 into the series circuit between the lamps 16 and battery 10. Inclusion of resistor 48 into the series circuit dims the lamps and drops the voltage at the normally open contact sufiiciently to permit the current flow from the capacitor through the lamps 16 to discharge the capacitor 40.

The above discussed cycle continually repeats itself flashing the lamps 16 on and off to give the usual turn signal indication. This continues until the arm of the switch 14 is positioned back to the normally open contact. With the arm in contact with the normally open contact the discharge path for the capacitor 40 through the lamps 16 is opened so that the capacitor can not be discharged to initiate another flashing cycle.

The period of the flashing cycle is determined by the operating time of the relay and the time constants of the various charging and discharging paths. To keep the period constant the thermistor 48 provides a negative coefiicient of resistance to compensate for the increase in relay operating time at the higher temperatures.

Resistor 48 in addition to providing a path to charge the capacitor 40, also improves the temperature stability of the transistor 38. Resistor 50 provides for a reverse bias on the transistor when the transistor is cut oil? and 3 thereby holds the transistor in a non-conducting state until the base-emitter junction is again forward biased.

It should be understood that this is intended to cover all changes and modifications of the described form of the structure herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

I claim:

1. A flasher that is used to flash a lamp load in a series circuit which includes the flasher, the lamp load, an electrical source of energy and a manually operable switch for making and breaking said series circuit, said flasher comprising:

(a) a relay having a winding and an armature, said armature when the winding is energized closing a connection between one terminal of said source and said switch and when the winding is deenergized opening such connection;

(b) a transistor connected in series with said winding across said source;

(0) a capacitor coupled to the transistor, said capacitor when charged rendering said transistor nonconducting and when discharged permitting the transistor to conduct;

(d) resistive means connecting said capacitor to said source through said armature when the winding is energized for charging the capacitor and connecting said capacitor to said switch for discharging the capacitor through the load when said switch is closed and said winding is deenergized, whereby when said switch is closed the capacitor is alternately charged and discharged to render said semiconductor alternately non-conductive and conductive to alternately deenergize and energize said winding and flash the lamp load.

2. The flasher according to claim 1 including a resistor connected between said resistive means and said source to provide a path for initially charging said capacitor.

3. The structure of claim 1 wherein said resistive means is temperature compensated to compensate for changes in the relays operating time.

References Cited by the Examiner UNITED STATES PATENTS 2,978,588 4/61 Mitchell et al 34033.1 X 3,113,242 12/63 Leeder 31S209 3,116,441 12/63 Greffers 317l48.5

DAVID J. GALVIN, Primary Examiner. 

1. A FLASHER THAT IS USED TO FLASH A LAMP LOAD IN A SERIES CIRCUIT WHICH INCLUDES THE FLASHER, THE LAMP LOAD, AN ELECTRICAL COURCE OF ENERGY AND A MANUALLY OPERABLE SWITCH FOR MAKING AND BREAKING SAID SERIES CIRCUIT, SAID FLASHER COMPRISING: (A) A RELAY HAVING A WINDING AND AN ARMATURE, SAID ARMATURE WHEN THE WINDING IS ENERGIZED CLOSING A CONNECTION BETWEEN ONE TERMINAL OF SAID SOURCE AND SAID SWITCH AND WHEN THE WINDING IS DEENERGIZED OPENING SUCH CONNECTION; (B) A TRANSISTOR CONNECTED IN SERIES WITH SAID WINDING ACROSS SAID SOURCE; (C) A CAPACITOR COUPLED TO THE TRANSISTOR, SAID CAPACITOR WHEN CHARGED RENDERING SAID TRANSISTOR NONCONDUCTING AND WHEN DISCHARGE PERMITTING THE TRANSISTOR TO CONDUCT; (D) RESISTIVE MEANS CONNECTING SAID CAPACITOR TO SAID SOURCE THROUGH SAID ARMATURE WHEN THE WINDING IS ENERGIZED FOR CHARGING THE CAPACITOR AND CONNECTING SAID CAPACITOR TO SAID SWITCH FOR DISCHARGING THE CAPACITOR THROUGH THE LOAD WHEN SAID SWITCH IS CLOSED AND SAID WINDING IS DEENERGIZED, WHEREBY WHEN SAID SWITCH IS CLOSED THE CAPACITOR IS ALTERNATELY CHARGED AND DISCHARGED TO RENDER SAID SEMICONDUCTOR ALTERNETALY NON-CONDUCTIVE AND CONDUCTIVE TO ALTERNATELY DEENERGIZED AND ENERGIZED SAID WINDING AND FLASH THE LAMP LOAD. 